This invention relates to implantable articles, such as joint prostheses, having an integral, textured bone engaging surface, and to methods for producing such articles.
There are known to exist many designs for and methods for manufacturing implantable articles, such as bone prostheses. Bone prostheses include components of artificial joints, such as elbows, hips, knees, and shoulders. An important consideration in the design and manufacture of virtually any implantable bone prosthesis is that the prosthesis be adequately affixed to bone after implantation within the body. In many instances it is important to implant the prosthesis without the use of bone cement and the like.
There are three generally accepted criteria for successful biological fixation of implantable articles within bone. First, the prostheses must be in contact with sound bone. Second, the prostheses must be in a close fit within a prepared cavity within bone. Third, there must be no perceptible motion (micromotion) between the prostheses and the bone under cyclic load bearing conditions. Recent attempts have been made to achieve optimal fixation by utilizing textured bone-engaging surfaces which encourage bone ingrowth.
Early designs of implantable articles relied upon the use of cements, such as polymethylmethacrylate, to anchor the implant. The use of such cements can have some advantages, for instance by providing an immediate and secure fixation that does not develop free play and lead to erosion of the joining bone faces postoperatively. However, the current trend is to use these cements to a lesser extent because of their tendency to lose effectiveness over time and due to the possibility that the cements will contribute to wear debris within a joint.
Recently, implantable bone prostheses have been designed so as to encourage the growth of hard tissue (i.e., bone) to be in intimate contact with the implant. The interaction of newly formed hard tissue in and around a textured surface of the implantable bone prosthesis has been found to provide good fixation of prostheses within the body. A greater degree of bone fixation can usually be achieved where bone engaging surfaces of an implantable bone prosthesis are more porous or irregular.
Porous or irregular surfaces can be provided in implantable articles by a variety of techniques. In some instances irregular surface patterns or surface features are formed in an implantable bone prosthesis by processing techniques such as casting, embossing, chemical etching, milling or machining. See, for example, U.S. Pat. Nos. 4,549,319 and 4,624,673. One drawback to using such techniques to provide irregular bone ingrowth surfaces on implantable bone prostheses is the significant amount of processing time required. These processing operations lead to delays in obtaining the finished product and significantly increase the cost of manufacturing the device.
Pore-forming surfaces can be formed on implantable bone prostheses by sintering small metal particles or powders to a surface of the prosthesis in a random pattern. Wire-based pads or grids can also be fused to implantable bone prostheses to provide a texture or surface relief features. A drawback of such techniques is that the components added to form the textured surface can become dislodged from the substrate of the prosthesis. Dislodgement of these components compromises the fixation mechanics of the implant and can contribute to the formation of wear debris. Further, the sintering step required to fuse texture-forming components to bone prostheses relies upon high temperature processing that could diminish the mechanical properties of the prostheses, distort the dimensions of the prostheses, and/or alter other properties of the materials from which the prostheses are made.
Additional techniques that are used to prepare textured surfaces for implantable articles, such as bone prostheses, include the use of laser energy to alter the surface of the implantable article. For example, U.S. Pat. Nos. 4,608,052; 4,673,409; and 5,246,530 teach various techniques for using a laser to form a plurality of discrete holes in the bone engaging surface of bone prostheses. The bone prostheses formed according to methods taught by these references have relatively regular surface features.
There is thus a need for implantable articles, such as bone prostheses, that have bone engaging surfaces that optimize successful biological fixation and that promote bone ingrowth. Accordingly, it is an object of the invention to provide an implantable article having a bone engaging surface that will achieve a close fit within a patient and promote considerable bone ingrowth. It is another object to provide a textured, bone engaging surface on an implantable article that will reduce stress on subsequent bone ingrowth. It is a further object to provide bone prostheses having textured, bone engaging surfaces that are integral with the bone prostheses. It is also an object to provide an economical method by which the bone engaging surface of implantable article may be textured. Yet another object is to provide a method of forming on an implantable article a textured bone-engaging surface without adversely affecting the metallurgical properties of the article. These and other objects will be apparent to those of ordinary skill in the art upon review of the following disclosure.